Modern aircraft gas turbines are of the turbofan type having large rotor blades usually at the forward end of the engine. The blades are termed "fan blades" and are utilized to accelerate air directed thereover in a manner much the same as a propeller.
Being located at the forward end of the engine, the blades are susceptible to foreign object damage as a result of debris picked up along the airport runway and ingested into the engine. Large birds are not an infrequent cause of fan damage. Damaged blades must be replaced to restore aerodynamic efficiency to the fan and to prevent destructive rotor imbalance.
Fan blade roots are conventionally formed to a dovetail cross-section geometry and extend from fore to aft across the rim of a supporting disk. The root attachments are usually canted circumferentially with respect to the centerline or axis of the engine. Blades of long span have one or more shrouds at an intermediate position along the span of the blades or at the blade tips. Such a shroud is formed of elements extending laterally from the pressure and suction sides of the blades into opposing relationship with the shroud elements of adjacent blades. In combination, the shroud elements form an annular ring when viewed in a direction along the axis of the engine. The plane of opposing relationship between adjacent shroud elements is nonparallel to the axis of the blade attachment, thereby locking each individual blade into the assembly.
To avoid the expense and necessity of removing all blades of a rotor stage in order to replace a single blade, scientists and engineers in the industry are searching for new blade concepts and techniques of this assembly.